CCIE Routing & Switching v5 Workbook -
CCIE R&S v5 Advanced Technology Labs -
LAN Switching
802.1q Dynamic Trunking
A Note On Section Initial Configuration Files: You must load the
initial configuration files for the section, named Basic Layer2
Switching, which can be found in
. Reference the Virtual Routers & Physical
Switches Diagram to complete this task.
Task
Configure all inter-switch links on SW2, SW3, and SW4 to be in dynamic auto state.
Configure all inter-switch links on SW1 to be in dynamic desirable state.
Configure the trunking encapsulation on SW1’s inter-switch links as static
802.1q.
For verification, ensure that:
SW2, SW3, and SW4 are negotiating 802.1q as the trunking encapsulation
to SW1.
SW1 is not negotiating 802.1q as the trunking encapsulation to SW2, SW3,
and SW4.
Configuration
SW1:
interface range FastEthernet0/19 - 24
switchport mode dynamic desirable
switchport trunk encapsulation dot1q
SW2:
interface range FastEthernet0/19 - 24
switchport mode dynamic auto
SW3:
interface range FastEthernet0/19 - 24
switchport mode dynamic auto
SW4:
interface range FastEthernet0/19 - 24
switchport mode dynamic auto
Verification
Similar to the previous case, SW1 is running in DTP desirable mode, so it is
negotiating trunking but now has its trunking encapsulation statically set to 802.1q.
SW1#show interface trunk
PortMode
Encapsulation StatusNative vlan
Fa0/19desirable
802.1q
trunking
1Fa0/20
desirable802.1q
trunking
1Fa0/21
desirable802.1q
trunking
1Fa0/22
desirable802.1q
trunking
1Fa0/23
desirable802.1q
trunking
1Fa0/24
desirable802.1q
trunking
1
<output omitted>
SW2, SW3, and SW4 must now agree to use dot1q trunking through DTP
negotiation, as seen in the n-802.1q output, which stands for negotiated-802.1q.
SW2#show interface trunk
PortModeEncapsulation StatusNative vlanFa0/23auton-802.1q
trunking
1Fa0/24auton-802.1q
trunking
1
<output omitted>
!
!SW3#show interface trunk
PortModeEncapsulation StatusNative vlanFa0/19auton-802.1q
trunking
1Fa0/20auton-802.1q
trunking
1
<output omitted>
!
!SW4#show interface trunk
PortModeEncapsulation StatusNative vlanFa0/21auton-802.1q
trunking
1Fa0/22auton-802.1q
trunking
1
<output omitted>
The fact that SW1 has its trunking protocol manually configured while all other
switches negotiate it can be seen in following output.
SW1#show interfaces fastEthernet0/19 switchport
Name: Fa0/19
Switchport: Enabled
Administrative Mode: dynamic desirable
Operational Mode: trunkAdministrative Trunking Encapsulation: dot1q
Operational Trunking Encapsulation: dot1q
Negotiation of Trunking: On
Access Mode VLAN: 1 (default)
Trunking Native Mode VLAN: 1 (default)
Administrative Native VLAN tagging: enabled
<output omitted>
!
!SW2#show interfaces fastEthernet0/19 switchport
Name: Fa0/19
Switchport: Enabled
Administrative Mode: dynamic auto
Operational Mode: static accessAdministrative Trunking Encapsulation: negotiate
Operational Trunking Encapsulation: native
Negotiation of Trunking: On
Access Mode VLAN: 1 (default)
Trunking Native Mode VLAN: 1 (default)
Administrative Native VLAN tagging: enabled
<output omitted>